Work machines, such as motor graders, dozers, compactors, pavers, profilers and scrapers, are used for geographic surface altering operations. The machines include a work implement, such as a surface altering blade, that is movably connected to a frame of the machine by one or more hydraulic motors or cylinders, or the work implement may be fixed to the machine frame. The position of the blade relative to the work surface must be accurately controlled to achieve the desired surface altering cut.
In motor graders, for example, the surface altering blade is movably connected to the grader frame by a pair of independently actuatable hydraulic lift cylinders that are mounted on either side of the machine frame. The hydraulic lift cylinders are independently extensible and retractable to move corresponding sides of the blade relative to the machine frame. Each side of the blade may be set by the operator to operate in either a "manual" or "automatic" mode of operation.
In the "manual" mode, the operator controls the elevational position of one or both sides of the blade through a pair of control levers mounted in the cab of the grader. Each control lever modulates a corresponding manual control valve connected to that lever. The pair of manual control valves are connected between a hydraulic fluid supply and a corresponding one of the hydraulic lift cylinders. The operator modulates the manual control valves to achieve the desired elevational position of the blade on the manually controlled side of the blade.
A pair of electrically actuatable control valves are also connected between the hydraulic fluid supply and a corresponding one of the hydraulic lift cylinders. The electrically actuatable control valves receive command signals from an implement controller to adjust the elevational position of one or both sides of the blade assigned to the "automatic" mode of operation.
During a grading operation, an operator may desire to adjust the elevational position of one side of the blade by modulating the manual control valve corresponding to each side of the blade. However, if the blade side to be adjusted is assigned to the "automatic" mode of operation, the operator's modulation of the manual control valve may contend with automatic operation of the automatic control valve on that side of the blade when both valves are operated simultaneously. When this occurs, the operator's input to the manual control valve may be resisted, and the desired adjustment in the blade's elevational position may not be achieved. Moreover, simultaneous operation of the manual and automatic control valves on the same side of the blade results in performance and reliability degradation of the motor grader's implement control system.
The present invention is directed to overcoming one or more of the problems as set forth above.